Seam provides a convenient method of remotely accessing components from a web page, using AJAX (Asynchronous
Javascript and XML). The framework for this functionality is provided with almost no up-front development effort -
your components only require simple annotating to become accessible via AJAX. This chapter describes the steps
required to build an AJAX-enabled web page, then goes on to explain the features of the Seam Remoting framework in
more detail.

25.1. Configuration

To use remoting, the Seam Resource servlet must first be configured in your web.xml file:

The next step is to import the necessary Javascript into your web page. There are a minimum of two scripts
that must be imported. The first one contains all the client-side framework code that enables remoting
functionality:

The second script contains the stubs and type definitions for the components you wish to call. It is
generated dynamically based on the local interface of your components, and includes type definitions for all of
the classes that can be used to call the remotable methods of the interface. The name of the script reflects the
name of your component. For example, if you have a stateless session bean annotated with
@Name("customerAction"), then your script tag should look like this:

Alternatively, you may use the s:remote tag to import the required Javascript. Separate each
component or class name you wish to import with a comma:

<s:remoteinclude="customerAction,accountAction"/>

25.2. The "Seam" object

Client-side interaction with your components is all performed via the Seam Javascript
object. This object is defined in remote.js, and you'll be using it to make asynchronous calls
against your component. It is split into two areas of functionality; Seam.Component contains
methods for working with components and Seam.Remoting contains methods for executing remote
requests. The easiest way to become familiar with this object is to start with a simple example.

25.2.1. A Hello World example

Let's step through a simple example to see how the Seam object works. First of all,
let's create a new Seam component called helloAction.

Note

If you are performing a persistence operation in the method marked @WebRemote you will
also need to add a @Transactional annotation to the method. Otherwise, your method would
execute outside of a transaction without this extra hint.That's because unlike a JSF request, Seam does not
wrap the remoting request in a transaction automatically.

Now for our web page - create a new page and import the
helloAction component:

<s:remoteinclude="helloAction"/>

To make this a fully interactive user experience, let's add a button to our page:

<buttononclick="javascript:sayHello()">Say Hello</button>

We'll also need to add some more script to make our button actually do something when it's clicked:

We're done! Deploy your application and browse to your page. Click the button, and enter a name when
prompted. A message box will display the hello message confirming that the call was successful. If you want to
save some time, you'll find the full source code for this Hello World example in Seam's
/examples/remoting/helloworld directory.

So what does the code of our script actually do? Let's break it down into smaller pieces. To start with,
you can see from the Javascript code listing that we have implemented two methods - the first method is
responsible for prompting the user for their name and then making a remote request. Take a look at the following
line:

The first section of this line, Seam.Component.getInstance("helloAction") returns a
proxy, or "stub" for our helloAction component. We can invoke the methods of our component
against this stub, which is exactly what happens with the remainder of the line: sayHello(name,
sayHelloCallback);.

What this line of code in its completeness does, is invoke the sayHello method of our
component, passing in name as a parameter. The second parameter,
sayHelloCallback isn't a parameter of our component's sayHello method,
instead it tells the Seam Remoting framework that once it receives the response to our request, it should pass
it to the sayHelloCallback Javascript method. This callback parameter is entirely optional,
so feel free to leave it out if you're calling a method with a void return type or if you
don't care about the result.

The sayHelloCallback method, once receiving the response to our remote request then pops
up an alert message displaying the result of our method call.

25.2.2. Seam.Component

The Seam.Component Javascript object provides a number of client-side methods for
working with your Seam components. The two main methods, newInstance() and
getInstance() are documented in the following sections however their main difference is
that newInstance() will always create a new instance of a component type, and
getInstance() will return a singleton instance.

25.2.2.1. Seam.Component.newInstance()

Use this method to create a new instance of an entity or Javabean component. The object returned by this
method will have the same getter/setter methods as its server-side counterpart, or alternatively if you wish
you can access its fields directly. Take the following Seam entity component for example:

customer.setFirstName("John");// Or you can set the fields directlycustomer.lastName = "Smith";

25.2.2.2. Seam.Component.getInstance()

The getInstance() method is used to get a reference to a Seam session bean component
stub, which can then be used to remotely execute methods against your component. This method returns a
singleton for the specified component, so calling it twice in a row with the same component name will return
the same instance of the component.

To continue our example from before, if we have created a new customer and we now wish
to save it, we would pass it to the saveCustomer() method of our
customerAction component:

Seam.Component.getInstance("customerAction").saveCustomer(customer);

25.2.2.3. Seam.Component.getComponentName()

Passing an object into this method will return its component name if it is a component, or
null if it is not.

25.2.3. Seam.Remoting

Most of the client side functionality for Seam Remoting is contained within the
Seam.Remoting object. While you shouldn't need to directly call most of its methods, there
are a couple of important ones worth mentioning.

25.2.3.1. Seam.Remoting.createType()

If your application contains or uses Javabean classes that aren't Seam components, you may need to create
these types on the client side to pass as parameters into your component method. Use the
createType() method to create an instance of your type. Pass in the fully qualified Java
class name as a parameter:

var widget = Seam.Remoting.createType("com.acme.widgets.MyWidget");

25.2.3.2. Seam.Remoting.getTypeName()

This method is the equivalent of Seam.Component.getComponentName() but for
non-component types. It will return the name of the type for an object instance, or null if
the type is not known. The name is the fully qualified name of the type's Java class.

25.3. Evaluating EL Expressions

Seam Remoting also supports the evaluation of EL expressions, which provides another convenient method for retrieving
data from the server. Using the Seam.Remoting.eval() function, an EL expression can be remotely
evaluated on the server and the resulting value returned to a client-side callback method. This function accepts two
parameters, the first being the EL expression to evaluate, and the second being the callback method to invoke with the
value of the expression. Here's an example:

In this example, the expression #{customers} is evaluated by Seam, and the value of the expression
(in this case a list of Customer objects) is returned to the customersCallback() method. It is
important to remember that the objects returned this way must have their types imported (via s:remote)
to be able to work with them in Javascript. So to work with a list of customer objects,
it is required to import the customer type:

<s:remoteinclude="customer"/>

25.4. Client Interfaces

In the configuration section above, the interface, or "stub" for our component is imported into our page
either via seam/resource/remoting/interface.js: or using the s:remote
tag:

By including this script in our page, the interface definitions for our component, plus any other components
or types that are required to execute the methods of our component are generated and made available for the
remoting framework to use.

There are two types of client stub that can be generated, "executable" stubs and "type" stubs. Executable
stubs are behavioural, and are used to execute methods against your session bean components, while type stubs
contain state and represent the types that can be passed in as parameters or returned as a result.

The type of client stub that is generated depends on the type of your Seam component. If the component is a
session bean, then an executable stub will be generated, otherwise if it's an entity or JavaBean, then a type stub
will be generated. There is one exception to this rule; if your component is a JavaBean (ie it is not a session
bean nor an entity bean) and any of its methods are annotated with @WebRemote, then an executable stub will be
generated for it instead of a type stub. This allows you to use remoting to call methods of your JavaBean
components in a non-EJB environment where you don't have access to session beans.

25.5. The Context

The Seam Remoting Context contains additional information which is sent and received as part of a remoting
request/response cycle. At this stage it only contains the conversation ID but may be expanded in the future.

25.5.1. Setting and reading the Conversation ID

If you intend on using remote calls within the scope of a conversation then you need to be able to read or
set the conversation ID in the Seam Remoting Context. To read the conversation ID after making a remote request
call Seam.Remoting.getContext().getConversationId(). To set the conversation ID before making a
request, call Seam.Remoting.getContext().setConversationId().

If the conversation ID hasn't been explicitly set with
Seam.Remoting.getContext().setConversationId(), then it will be automatically assigned the
first valid conversation ID that is returned by any remoting call. If you are working with multiple conversations
within your page, then you may need to explicitly set the conversation ID before each call. If you are working
with just a single conversation, then you don't need to do anything special.

25.5.2. Remote calls within the current conversation scope

In some circumstances it may be required to make a remote call within the scope of the
current view's conversation. To do this, you must explicitly set the conversation ID to that
of the view before making the remote call. This small snippet of JavaScript will set the
conversation ID that is used for remoting calls to the current view's conversation ID:

Seam.Remoting.getContext().setConversationId( #{conversation.id} );

25.6. Batch Requests

Seam Remoting allows multiple component calls to be executed within a single request. It is recommended that
this feature is used wherever it is appropriate to reduce network traffic.

The method Seam.Remoting.startBatch() will start a new batch, and any component calls
executed after starting a batch are queued, rather than being sent immediately. When all the desired component
calls have been added to the batch, the Seam.Remoting.executeBatch() method will send a single
request containing all of the queued calls to the server, where they will be executed in order. After the calls
have been executed, a single response containining all return values will be returned to the client and the
callback functions (if provided) triggered in the same order as execution.

If you start a new batch via the startBatch() method but then decide you don't want to
send it, the Seam.Remoting.cancelBatch() method will discard any calls that were queued and
exit the batch mode.

To see an example of a batch being used, take a look at /examples/remoting/chatroom.

25.7. Working with Data types

25.7.1. Primitives / Basic Types

This section describes the support for basic data types. On the server side these values are generally
compatible with either their primitive type or their corresponding wrapper class.

25.7.1.1. String

25.7.1.2. Number

There is support for all number types supported by Java. On the client side, number values are always
serialized as their String representation and then on the server side they are converted to the correct
destination type. Conversion into either a primitive or wrapper type is supported for Byte,
Double, Float, Integer, Long and
Short types.

25.7.1.3. Boolean

Booleans are represented client side by Javascript Boolean values, and server side by a Java boolean.

25.7.2. JavaBeans

In general these will be either Seam entity or JavaBean components, or some other non-component class. Use
the appropriate method (either Seam.Component.newInstance() for Seam components or
Seam.Remoting.createType() for everything else) to create a new instance of the object.

It is important to note that only objects that are created by either of these two methods should be used as
parameter values, where the parameter is not one of the other valid types mentioned anywhere else in this
section. In some situations you may have a component method where the exact parameter type cannot be determined,
such as:

In this case you might want to pass in an instance of your myWidget component, however
the interface for myAction won't include myWidget as it is not directly
referenced by any of its methods. To get around this, MyWidget needs to be explicitly
imported:

<s:remoteinclude="myAction,myWidget"/>

This will then allow a myWidget object to be created with
Seam.Component.newInstance("myWidget"), which can then be passed to
myAction.doSomethingWithObject().

25.7.3. Dates and Times

Date values are serialized into a String representation that is accurate to the millisecond. On the client
side, use a Javascript Date object to work with date values. On the server side, use any
java.util.Date (or descendent, such as java.sql.Date or
java.sql.Timestamp class.

25.7.4. Enums

On the client side, enums are treated the same as Strings. When setting the value for an enum parameter,
simply use the String representation of the enum. Take the following component as an example:

To call the paint() method with the color red, pass the parameter
value as a String literal:

Seam.Component.getInstance("paintAction").paint("red");

The inverse is also true - that is, if a component method returns an enum parameter (or contains an enum
field anywhere in the returned object graph) then on the client-side it will be represented as a String.

25.7.5. Collections

25.7.5.1. Bags

Bags cover all collection types including arrays, collections, lists, sets, (but excluding Maps - see the
next section for those), and are implemented client-side as a Javascript array. When calling a component
method that accepts one of these types as a parameter, your parameter should be a Javascript array. If a
component method returns one of these types, then the return value will also be a Javascript array. The
remoting framework is clever enough on the server side to convert the bag to an appropriate type for the
component method call.

25.7.5.2. Maps

As there is no native support for Maps within Javascript, a simple Map implementation is provided with
the Seam Remoting framework. To create a Map which can be used as a parameter to a remote call, create a new
Seam.Remoting.Map object:

var map = new Seam.Remoting.Map();

This Javascript implementation provides basic methods for working with Maps: size(),
isEmpty(), keySet(), values(),
get(key), put(key, value), remove(key) and
contains(key). Each of these methods are equivalent to their Java counterpart. Where the
method returns a collection, such as keySet() and values(), a Javascript
Array object will be returned that contains the key or value objects (respectively).

25.8. Debugging

To aid in tracking down bugs, it is possible to enable a debug mode which will display the contents of all
the packets send back and forth between the client and server in a popup window. To enable debug mode, either
execute the setDebug() method in Javascript:

Seam.Remoting.setDebug(true);

Or configure it via components.xml:

<remoting:remotingdebug="true"/>

To turn off debugging, call setDebug(false). If you want to write your own messages to the
debug log, call Seam.Remoting.log(message).

25.9. Handling Exceptions

When invoking a remote component method, it is possible to specify an exception handler which will process
the response in the event of an exception during component invocation. To specify an exception handler function,
include a reference to it after the callback parameter in your JavaScript:

25.10.3. A Custom Loading Indicator

It is also possible to override the loading indicator to display an animated icon, or anything else that
you want. To do this override the displayLoadingMessage() and
hideLoadingMessage() messages with your own implementation:

25.11. Controlling what data is returned

When a remote method is executed, the result is serialized into an XML response that is returned to the
client. This response is then unmarshaled by the client into a Javascript object. For complex types (i.e.
Javabeans) that include references to other objects, all of these referenced objects are also serialized as part
of the response. These objects may reference other objects, which may reference other objects, and so forth. If
left unchecked, this object "graph" could potentially be enormous, depending on what relationships exist between
your objects. And as a side issue (besides the potential verbosity of the response), you might also wish to
prevent sensitive information from being exposed to the client.

Seam Remoting provides a simple means to "constrain" the object graph, by specifying the
exclude field of the remote method's @WebRemote annotation. This field
accepts a String array containing one or more paths specified using dot notation. When invoking a remote method,
the objects in the result's object graph that match these paths are excluded from the serialized result packet.

25.11.1. Constraining normal fields

If your remote method returns an instance of Widget, but you don't want to expose the
secret field because it contains sensitive information, you would constrain it like this:

@WebRemote(exclude ={"secret"})publicWidget getWidget();

The value "secret" refers to the secret field of the returned object. Now, suppose that
we don't care about exposing this particular field to the client. Instead, notice that the
Widget value that is returned has a field child that is also a
Widget. What if we want to hide the child's secret
value instead? We can do this by using dot notation to specify this field's path within the result's object
graph:

@WebRemote(exclude ={"child.secret"})publicWidget getWidget();

25.11.2. Constraining Maps and Collections

The other place that objects can exist within an object graph are within a Map or some
kind of collection (List, Set, Array, etc). Collections
are easy, and are treated like any other field. For example, if our Widget contained a list
of other Widgets in its widgetList field, to constrain the
secret field of the Widgets in this list the annotation would look like
this:

@WebRemote(exclude ={"widgetList.secret"})publicWidget getWidget();

To constrain a Map's key or value, the notation is slightly different. Appending
[key] after the Map's field name will constrain the
Map's key object values, while [value] will constrain the value object
values. The following example demonstrates how the values of the widgetMap field have their
secret field constrained:

25.11.3. Constraining objects of a specific type

There is one last notation that can be used to constrain the fields of a type of object no matter where in
the result's object graph it appears. This notation uses either the name of the component (if the object is a
Seam component) or the fully qualified class name (only if the object is not a Seam component) and is expressed
using square brackets:

@WebRemote(exclude ={"[widget].secret"})publicWidget getWidget();

25.11.4. Combining Constraints

Constraints can also be combined, to filter objects from multiple paths within the object graph:

25.12. Transactional Requests

By default there is no active transaction during a remoting request, so if you wish to perform database updates
during a remoting request, you need to annotate the @WebRemote method with
@Transactional, like so:

25.13. JMS Messaging

Seam Remoting provides experimental support for JMS Messaging. This section describes the JMS support that is
currently implemented, but please note that this may change in the future. It is currently not recommended that
this feature is used within a production environment.

25.13.1. Configuration

Before you can subscribe to a JMS topic, you must first configure a list of the topics that can be
subscribed to by Seam Remoting. List the topics under
org.jboss.seam.remoting.messaging.subscriptionRegistry.allowedTopics in
seam.properties, web.xml or components.xml.

The Seam.Remoting.subscribe() method accepts two parameters, the first being the name of
the JMS Topic to subscribe to, the second being the callback function to invoke when a message is received.

There are two types of messages supported, Text messages and Object messages. If you need to test for the
type of message that is passed to your callback function you can use the instanceof operator
to test whether the message is a Seam.Remoting.TextMessage or
Seam.Remoting.ObjectMessage. A TextMessage contains the text value in
its text field (or alternatively call getText() on it), while an
ObjectMessage contains its object value in its value field (or call its
getValue() method).

25.13.3. Unsubscribing from a Topic

To unsubscribe from a topic, call Seam.Remoting.unsubscribe() and pass in the topic
name:

Seam.Remoting.unsubscribe("topicName");

25.13.4. Tuning the Polling Process

There are two parameters which you can modify to control how polling occurs. The first one is
Seam.Remoting.pollInterval, which controls how long to wait between subsequent polls for
new messages. This parameter is expressed in seconds, and its default setting is 10.

The second parameter is Seam.Remoting.pollTimeout, and is also expressed as seconds. It
controls how long a request to the server should wait for a new message before timing out and sending an empty
response. Its default is 0 seconds, which means that when the server is polled, if there are no messages ready
for delivery then an empty response will be immediately returned.

Caution should be used when setting a high pollTimeout value; each request that has to
wait for a message means that a server thread is tied up until a message is received, or until the request times
out. If many such requests are being served simultaneously, it could mean a large number of threads become tied
up because of this reason.

It is recommended that you set these options via components.xml, however they can be overridden via
Javascript if desired. The following example demonstrates how to configure the polling to occur much more
aggressively. You should set these parameters to suitable values for your application:

Via components.xml:

<remoting:remotingpoll-timeout="5"poll-interval="1"/>

Via JavaScript:

// Only wait 1 second between receiving a poll response and sending the next poll request.Seam.Remoting.pollInterval = 1;// Wait up to 5 seconds on the server for new messagesSeam.Remoting.pollTimeout = 5;